1. Field of the Invention
The present invention relates to a system and apparatus to convey finely divided particulate matter with suppressed formation of airborne dust.
2. Background of the Related Art
Seasonings are often applied to processed foods such as, for example, potato chips, to enhance the consumers' taste experience by providing consistent flavoring. Seasonings are generally furnished to food processors in finely divided particulate form and packaged in bulk. Sacks of seasoning may weigh 35 to 50 lbs. (15.8 to 22.7 kg). The finely divided particulate form of bulk seasonings may be characterized as a powder with particle size ranging from about 3 microns up to about 3 mm. Some seasonings may consist of generally uniformly-sized particles while other seasonings may consist of particles ranging in size from large to small particles. The latter seasonings may segregate during transport.
A food processing plant for producing prepared foods generally has several processing lines producing food products that differ in size, shape and/or flavor. One or more seasonings may be required for a particular food product. Seasonings are provided to the processing line for being applied to the product at a seasoning station. Each seasoning station includes a bin to receive and store a supply of the seasoning to be applied to a food product on that processing line. The seasoning is generally dispensed from the bin and onto the product with the assistance of gravity. The supply of seasoning stored in the bin must be periodically replenished.
The intervals between replenishment of the seasoning stored in several bins on several processing lines in a plant will vary from bin to bin according to the size of the bin and the rate at which seasoning is dispensed from the bin for being applied to a food product. A seasoning replenishment container may remain idle between replenishments. Some seasonings tend to segregate during storage, while other seasonings may coalesce within the replenishment container to form clumps. These problems are generally remedied by plant personnel by mixing or stirring the seasoning within the replenishment container to restore the seasoning to a condition suitable for replenishing the bins on the processing lines. Plant personnel may apply blows on the side of the replenishment container, stir the seasoning using an implement or physically shake the replenishment container to disturb the contents. These solutions are unsatisfactory and may result in an uneven seasoning distribution on the product and lowered consumer satisfaction.
Bins from which seasoning is dispensed onto a food product on a processing line in a plant are generally elevated well above the plant floor to accommodate a gradually descending process line. This sloping configuration is incorporated into processing lines to provide for the movement of a food product at a uniform rate that enables consistent and uniform seasoning application. Tumblers, conveyors and bagging machines are generally structured to use gravity to move the food product from a higher elevation to a lower elevation. This arrangement requires that the bin for storing seasoning at each processing line be elevated well above the plant floor, and that seasoning from the replenishment container be elevated en route to the bin. Conventional equipment for elevating and conveying bulk seasonings include screw conveyors, drag conveyors and bucket elevators.
Seasonings generally comprise organic materials that may adhere to a variety of surfaces. Seasoning replenishment containers should be easily cleaned so that the same equipment can be used to convey different seasonings and used to produce different food products with an insignificant amount of seasoning carry over. Conventional equipment for elevating and conveying bulk seasonings are difficult to clean and require large radius turns and/or have large equipment footprints. In a food processing plant having several processing lines requiring several different seasonings, it is desirable to have a replenishment container that is easily cleaned and portable to provide for the convenient replenishment of seasoning in the bin of each processing line with minimum obstruction of the plant floor.
Handling of particulate matter such as seasonings risks generating particulate dust within the food processing plant environment. It is desirable to minimize the amount of dust generated within the plant. Pneumatic conveying systems for seasonings exacerbate the dust risk. The amount of particulate dust created using pneumatic conveying systems to transfer particulate matter is exponentially related to the volume and the velocity of the air used to convey the seasoning. Pneumatic conveying systems use a very large volume of moving air for each unit of mass of the seasoning moved by the system. The corresponding density of the conveyed air/seasoning stream is very low due to the use of large volumes of propulsive air mixed with a small mass of seasoning. In addition, pneumatic conveying systems cause a substantial amount of segregation and produce a very large amount of dust at the receiving bin of the conveying system.
A conveying system may be assessed using the phase density which is the mass, in pounds (or kilograms), of particulate matter moving past a given point in a minute divided by the volume of air used to convey that mass of particulate matter. A low phase density in a conveying system means a low efficiency, high energy costs to move a large mass rate of air, high segregation of the particulate matter from the moving stream of air and seasoning, high product or seasoning damage, and a large amount of unwanted dust generated within the plant. Conversely, a high phase density means a high efficiency, substantially lower energy costs, less segregation of the particulate matter from the moving stream of air and seasoning, low product and seasoning damage, and substantially less dust generated within the plant.
It has long been recognized by those using pneumatic conveyance systems that wear on components of a particulate matter conveyor system increases exponentially with the velocity. Empirical studies show that wear increases by a factor equal to the increased velocity raised to an exponent of 2.8. Depending on particle friability, size and shape, the damage to the seasoning particles increases by roughly the same exponential rate. It is therefore desirable to increase the phase density and lower the conveyance velocity to achieve exponentially reduced component wear and exponentially reduced seasoning damage.